1. Field of the Invention
The present invention relates to a method for packing, into a fixed bed type reactor, a catalyst containing at least molybdenum and iron, used in the gas-phase catalytic oxidation of propylene, isobutylene, tert-butyl alcohol (hereinafter abbreviated to TBA) or methyl tert-butyl ether (hereinafter abbreviated to MTBE) with molecular oxygen to synthesize an unsaturated aldehyde and an unsaturated carboxylic acid both corresponding to the raw material used. The present invention relates also to a process for producing an unsaturated aldehyde and an unsaturated carboxylic acid in a reactor wherein a catalyst is packed by the above method.
2. Description of Related Art
Generally in a fixed bed type reactor, there is employed a method for packing of catalyst which comprises dropping, into the reactor from its top, a shaped catalyst or a supported catalyst, used in the gas-phase catalytic oxidation of propylene, isobutylene, TBA or MTBE with molecular oxygen. When, in the catalytic oxidation, a raw material gas is passed through the reactor, a pressure loss appears owing to the packed molded catalyst or supported catalyst and this pressure loss becomes larger owing to the pulverization or disintegration of catalyst brought about by the physical impact which the catalyst receives when dropped.
In the gas-phase catalytic oxidation of propylene, isobutylene, TBA or MTBE using molecular oxygen, the reaction is carried out at a low pressure in order to suppress successive oxidation, whereby an intended unsaturated aldehyde and an intended carboxylic acid both corresponding to the raw material used can be produced at high yields. In carrying out the gas-phase catalytic oxidation on an industrial scale, however, a pressure loss appears and it becomes larger for the reasons mentioned above; therefore, it is difficult to carry out the reaction at a low pressure.
In an attempt to keeping low the pressure loss caused by catalyst, JP-B-62-36739, JP-B-62-36740, etc. disclose a method for keeping low the pressure loss by using a shaped catalyst of appropriately selected shape. Use of a shaped catalyst of appropriately selected shape alone cannot keep the pressure loss sufficiently low, and an effective method for keeping low the pressure loss is being looked for. Further, JP-A-4-119901 discloses mixed use of a reforming catalyst and an auxiliary packing material in the reforming of a hydro-carbon type fuel and shows, in the Examples, a case of using stainless steel-made Raschig rings as an auxiliary packing material. In this case, however, the auxiliary packing material has a bulk volume of about 0.1 time that of the reforming catalyst and, when their mixture is dropped into a reactor from its top, the catalyst and the auxiliary packing material are packed in the reactor in a nonuniformly mixed state. Although an auxiliary packing material has, in an exothermic reaction such as oxidation reaction or the like, a role of diluent capable of preventing the generation of hot spots, the packing of the catalyst and the auxiliary packing material in a nonuniformly mixed state generates hot spots.